"The Siphonaptera" is a nursery rhyme

Nursery rhyme

The term nursery rhyme is used for "traditional" poems for young children in Britain and many other countries, but usage only dates from the 19th century and in North America the older ‘Mother Goose Rhymes’ is still often used.-Lullabies:...

, sometimes referred to as Fleas.

Big fleas have little fleas,
Upon their backs to bite 'em,
And little fleas have lesser fleas,
and so, ad infinitum.

Sometimes a second verse appears, with lines such as

And the great fleas, themselves, in turn
Have greater fleas to go on;
While these again have greater still,
And greater still, and so on.

The rhyme is closely based on lines by Jonathan Swift

Jonathan Swift

Jonathan Swift was an Irish satirist, essayist, political pamphleteer , poet and cleric who became Dean of St...

 from his long satirical poem "On Poetry: a Rhapsody" (1733):


The vermin only teaze and pinch
Their foes superior by an inch.
So, naturalists observe, a flea
Has smaller fleas that on him prey;
And these have smaller still to bite 'em,
And so proceed ad infinitum.


Lewis F. Richardson adapted the poem to meteorology, specifically discussing fractal wind patterns:

Big whorls have little whorls
That feed on their velocity

Angular velocity

In physics, the angular velocity is a vector quantity which specifies the angular speed of an object and the axis about which the object is rotating. The SI unit of angular velocity is radians per second, although it may be measured in other units such as degrees per second, revolutions per...

;
And little whorls have lesser whorls
And so on to viscosity

Viscosity

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

.